1. Field of the Invention
The present invention relates to an injection apparatus.
2. Description of the Related Art
Conventionally, in an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the resin. The molten resin is then cooled and solidified within the cavity so as to obtain a molded article.
The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen and a movable platen. The movable platen is advanced and retracted by a mold clamping cylinder, to thereby perform mold closing, mold clamping, and mold opening.
The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. Further, a screw is disposed within the heating cylinder such that the screw can be rotated and can be advanced and retracted. When the screw is advanced by a drive section disposed at the rear,end of the screw, the resin is injected from the injection nozzle, and when the screw is retracted by the drive section, the resin is metered.
The drive section comprises a front plate for supporting the heating cylinder; a rear plate disposed a predetermined distance away from the front plate; guide bars disposed between and supported by the front plate and the rear plate; and a movable plate disposed to be slidable along the guide bars. The above-described screw is rotatably supported by the movable plate. A ball screw shaft and a ball nut are disposed between the front plate and the movable plate. When an injection motor is driven to rotate the ball screw shaft or the ball nut, the movable plate is advanced or retracted.
FIG. 1 is a sectional view of a drive section of a conventional injection apparatus; FIG. 2 is a side view of the drive section of the conventional injection apparatus; and FIG. 3 is a schematic diagram showing the concept of the drive section of the conventional injection apparatus.
In these drawings, reference numeral 12 denotes a heating cylinder, 22 denotes a screw, 31 denotes a slide table slidably disposed on an unillustrated frame, and 34 denotes a stationary plate fixed to the slide table 31. The rear end (right end in FIG. 1) of the heating cylinder 12 is fixed to the stationary plate 34. Further, a movable plate 36 is disposed such that the movable plate 36 can be advanced and retracted relative to the stationary plate 34.
A screw support shaft 38 is disposed at the approximate center of the movable plate 36 and is rotatably supported thereby via bearings 41 and 42. The rear end of the screw 22 is fixed to the screw support shaft 38, and a driven pulley 43 is fixed to the rear end of the screw support shaft 38.
An unillustrated metering motor is attached to one side surface S1 of the movable plate 36, and an unillustrated drive pulley is attached to the output shaft of the metering motor. An unillustrated timing belt extends between and is wound, under tension, around the drive pulley and the driven pulley 43. The bearing 42 assumes the form of a thrust bearing in order to bear injection force that acts on the screw 22 upon injection.
Two parallel ball screw shafts 45 are disposed at positions in the vicinity of the circumferential edge of the movable plate 36 and are rotatably supported by the movable plate 36 via bearings 46. Each of the ball screw shafts 45 has a screw portion 48 and a shaft portion 49 projecting from the rear end (right end in FIG. 1) of the screw portion 48. The shaft portion 49 penetrates a hole 36a formed in the movable plate 36 and extends rearward (rightward in FIG. 1), and a driven pulley 51 is attached to the rear end of the shaft portion 49. The screw portion 48 penetrates a hole 34a formed in the stationary plate 34 and extends frontward (leftward in FIG. 1) to be screw-engaged with a ball nut 52 attached to the stationary plate 34. The ball nut 52 has a flange portion 53 at its front end (left end in FIG. 1) and is fixed to the stationary plate 34 by use of unillustrated bolts that penetrate the flange portion 53. Reference numeral 55 denotes a press plate for pressing the bearing 46.
An injection motor 75 is attached to the approximate center of the other side surface S2 of the movable plate 36. A drive pulley 76 is attached to the output shaft 75a of the injection motor 75, and a timing belt 77 extends between and is wound, under tension, around the drive pulley 76 and the driven pulley 51.
Next, operation of the injection apparatus having the above-described structure will be described.
In a metering stage, when the screw 22 is rotated through driving of the metering motor, resin falls from an unillustrated hopper and enters the heating cylinder 12, so that the resin is advanced (moved to leftward in FIG. 1) within the heating cylinder 12. Subsequently, the screw 22 is retracted (moved to rightward in FIG. 1) while being rotated.
An unillustrated heater is disposed to surround the heating cylinder 12 and is adapted to heat the heating cylinder 12 to thereby melt the resin within the heating cylinder 12. Therefore, when the screw 22 is retracted by a predetermined amount, while being rotated, molten resin for one shot is accumulated on the front side of an unillustrated screw head.
In a subsequent injection step, when the screw 22 is advanced through driving of the injection motor 75, the resin accumulated on the front side of the screw head is injected from an unillustrated injection nozzle attached to the front end of the heating cylinder 12 and is charged into a cavity of an unillustrated mold apparatus.
In such a conventional injection apparatus, since the two ball screw shafts 45 are rotated at the same circumferential speed through driving of the single injection motor 75, the diameters of the respective driven pulleys 51 must be made equal in order to make their reduction ratios equal. When the diameters of the driven pulleys 51 are increased in order to increase their reduction ratios, their inertia increases, with the result that the performance of the injection apparatus is lowered. Further, the timing belt 77 must have a longer length. When xcex81 represents an effective angle of engagement of the drive pulley 76 which establishes meshing engagement for transmitting rotation from the injection motor 75 to the timing belt 77, and xcex82 and xcex83 respectively represent effective angles of engagement of the driven pulleys 51 which establish meshing engagements for transmitting rotation from the timing belt 77 to the respective ball screw shafts 45, the following equation is satisfied.
xcex81+xcex82+xcex83=360xc2x0
When the drive-side effective angle xcex81 is small, as shown in FIG. 3, the rotation transmitted from the injection motor 75 cannot be transmitted to the timing belt 77 in a reliable manner. Therefore, rotation cannot be transmitted to the ball screw shafts 45 in a stable manner, resulting in a deterioration in the performance of the injection apparatus.
The inter-axis distance L1 between the drive pulley 76 and the driven pulleys 51 or the widths of the driven pulleys 51, the drive pulley 76, and the timing belt 77 may be increased in order to increase the drive-side effective angle xcex81.
However, when the inter-axis distance L1 is increased, the size of the injection machine increases, because the width of the movable plate 36 or the depth of the drive section must be increased. When the widths of the driven pulleys 51, the drive pulley 76, and the timing belt 77 are increased, noise generated when the injection motor 75 is driven at high speed increases.
An injection apparatus is provided which comprises a cylinder section; a stationary plate fixed to a rear end of said cylinder section; a movable plate movable relative to said stationary plate; an injection member disposed within said cylinder section such that said injection member can be advanced and retracted, a rear end of said injection member being rotatably supported by said movable plate; drive means for generating a rotation; a plurality of conversion means each disposed between said stationary plate and said movable plate and adapted to covert a rotational force to a thrust force; transmission means disposed between said drive means and only a first conversion means of said plurality of conversion means for transmitting the rotation generated by said drive means to said first conversion means; and synchronization means for synchronizing rotation of said first conversion means with rotation of the remaining conversion means.
An injection apparatus is provided which comprises an injection apparatus comprising a first support; a second support, moveable relative to said first support; a cylinder fixed to said first support; a screw, rotatably connected to said second support, disposed within said cylinder; at least first and second ball and screw mechanisms connecting said first support to said second support, operable to move said second support relative to said first support; a motor having a rotatable output shaft; a first transmission transmitting a rotation of the output shaft of the motor to only said first ball and screw mechanism; and a second transmission transmitting a rotation of the first ball and screw mechanism to at least said second ball and screw mechanism.
A method of operating an injection apparatus including a cylinder fixed to a first support and a metering screw rotatably connected to a second support and disposed within said cylinder is provided, comprising rotating a driving pulley with a motor; rotating a first screw through a belt connection from said driving pulley to a driven pulley fixed to said first screw; rotating at least a second screw through a transmission connected between said first screw and said second screw; and moving said first support relative to said second support via forces exerted by said first and second screws respectively on first and second nuts disposed about said first and second screws.